Structural and Functional Evidence Indicates Selective Oxygen Signaling in Caldanaerobacter subterraneus H-NOX

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• 作者：Charles W. Hespen ; Joel J. Bruegger ; Christine M. Phillips-Piro ; Michael A. Marletta
• 刊名：ACS Chemical Biology
• 出版年：2016
• 出版时间：August 19, 2016
• 年：2016
• 卷：11
• 期：8
• 页码：2337-2346
• 全文大小：580K
• 年卷期：0
• ISSN：1554-8937

文摘

Acute and specific sensing of diatomic gas molecules is an essential facet of biological signaling. Heme nitric oxide/oxygen binding (H-NOX) proteins are a family of gas sensors found in diverse classes of bacteria and eukaryotes. The most commonly characterized bacterial H-NOX domains are from facultative anaerobes and are activated through a conformational change caused by formation of a 5-coordinate Fe(II)-NO complex. Members of this H-NOX subfamily do not bind O₂ and therefore can selectively ligate NO even under aerobic conditions. In contrast, H-NOX domains encoded by obligate anaerobes do form stable 6-coordinate Fe(II)-O₂ complexes by utilizing a conserved H-bonding network in the ligand-binding pocket. The biological function of O₂-binding H-NOX domains has not been characterized. In this work, the crystal structures of an O₂-binding H-NOX domain from the thermophilic obligate anaerobe Caldanaerobacter subterraneus (Cs H-NOX) in the Fe(II)-NO, Fe(II)-CO, and Fe(II)-unliganded states are reported. The Fe(II)-unliganded structure displays a conformational shift distinct from the NO-, CO-, and previously reported O₂-coordinated structures. In orthogonal signaling assays using Cs H-NOX and the H-NOX signaling effector histidine kinase from Vibrio cholerae (Vc HnoK), Cs H-NOX regulates Vc HnoK in an O₂-dependent manner and requires the H-bonding network to distinguish O₂ from other ligands. The crystal structures of Fe(II) unliganded and NO- and CO-bound Cs H-NOX combined with functional assays herein provide the first evidence that H-NOX proteins from obligate anaerobes can serve as O₂ sensors.